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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="asio.history"></a><a class="link" href="history.html" title="Revision History">Revision History</a>
</h2></div></div></div>
<h4>
<a name="asio.history.h0"></a>
      <span><a name="asio.history.asio_1_12_2"></a></span><a class="link" href="history.html#asio.history.asio_1_12_2">Asio
      1.12.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed a problem with the detection of <code class="computeroutput">std::future</code> availability
          with libstdc++.
        </li>
<li class="listitem">
          Fixed compile error in regex overload of <code class="computeroutput">read_until</code>.
        </li>
<li class="listitem">
          Fixed a timer heap corruption issue that can occur when moving a cancelled
          timer.
        </li>
<li class="listitem">
          Fixed detection of <code class="computeroutput">std::experimental::string_view</code> and <code class="computeroutput">std::string_view</code>
          with newer clang/libc++.
        </li>
<li class="listitem">
          Fixed MSVC version detection for availability of <code class="computeroutput">std::invoke_result</code>.
        </li>
<li class="listitem">
          Fixed the buffer sequence traits to test the new requirements, if <code class="computeroutput">decltype</code>
          is available.
        </li>
<li class="listitem">
          Fixed an MSVC issue when building with exceptions disabled.
        </li>
<li class="listitem">
          Added SSL context options for TLS v1.3.
        </li>
<li class="listitem">
          Added a compile-time test for TLS v1 support.
        </li>
<li class="listitem">
          Fixed the macro used to test for TLS v1.2 support.
        </li>
<li class="listitem">
          Prevented global objects from being created once per thread on Windows.
        </li>
<li class="listitem">
          Fixed a crash when using <code class="computeroutput">size()</code>, <code class="computeroutput">max_size()</code> or
          <code class="computeroutput">empty()</code> on default-constructed resolver results.
        </li>
<li class="listitem">
          Changed to move the return value in basic_resolver_results::begin() to
          avoid copying.
        </li>
<li class="listitem">
          Enabled move support for the Intel Compiler.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">std::string_view</code> detection issue when using clang-cl.
        </li>
<li class="listitem">
          Fixed the handler tracking operation name for <code class="computeroutput">io_context::executor_type::dispatch</code>.
        </li>
<li class="listitem">
          Fixed a buffer overflow that could occur when parsing an address string
          with a 64-bit scope id.
        </li>
<li class="listitem">
          Added examples showing how to write composed operations.
        </li>
<li class="listitem">
          Added C++11 versions of the Timeouts, Timers, SOCKS4 and SSL examples.
        </li>
<li class="listitem">
          Fixed minor issues in documentation and examples.
        </li>
</ul></div>
<h4>
<a name="asio.history.h1"></a>
      <span><a name="asio.history.asio_1_12_1"></a></span><a class="link" href="history.html#asio.history.asio_1_12_1">Asio
      1.12.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added missing const qualifier to <code class="computeroutput">basic_socket_acceptor::get_option</code>.
        </li>
<li class="listitem">
          Worked around a parsing error that occurs with some versions of gcc.
        </li>
<li class="listitem">
          Fixed broken code samples in tutorial.
        </li>
<li class="listitem">
          Added new experimental features. (Note that "experimental" features
          may be changed without notice in subsequent releases.)
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Added <code class="computeroutput">experimental::detached</code> completion token.
              </li>
<li class="listitem">
                Added <code class="computeroutput">experimental::redirect_error</code> completion token.
              </li>
<li class="listitem">
                Added <code class="computeroutput">experimental::co_spawn</code> facility for integration
                with the coroutines technical specification.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Updated timeout examples to use latest features.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Used <code class="computeroutput">asio::steady_timer</code> rather than <code class="computeroutput">asio::deadline_timer</code>.
              </li>
<li class="listitem">
                Used <code class="computeroutput">asio::dynamic_buffer</code> rather than <code class="computeroutput">asio::streambuf</code>.
              </li>
<li class="listitem">
                Used timed <code class="computeroutput">asio::io_context::run_for()</code> function for
                blocking clients.
              </li>
<li class="listitem">
                Added example showing a custom completion token for blocking with
                timeouts.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed unit tests to compile when <code class="computeroutput">(BOOST_)ASIO_NO_DEPRECATED</code>
          is defined.
        </li>
<li class="listitem">
          Changed socket iostreams to use chrono by default, to fix compatibility
          with the Networking TS. Define <code class="computeroutput">(BOOST_)ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM</code>
          to enable the old Boost.Date_Time interface in <code class="computeroutput">basic_socket_streambuf</code>
          and <code class="computeroutput">basic_socket_iostream</code>.
        </li>
<li class="listitem">
          Updated examples to use chrono rather than Boost.Date_Time.
        </li>
<li class="listitem">
          Fixed an incorrect member function detector in the <code class="computeroutput">is_dynamic_buffer</code>
          trait.
        </li>
<li class="listitem">
          Fixed an <code class="computeroutput">async_result</code> incompatibility with deprecated <code class="computeroutput">handler_type</code>.
        </li>
<li class="listitem">
          Added a missing move optimisation in the SSL stream implementation.
        </li>
<li class="listitem">
          Fixed incorrect <code class="computeroutput">basic_resolver_results::value_type</code> typedef.
        </li>
<li class="listitem">
          Fixed a compile error with some OpenSSL versions when <code class="computeroutput">SSL_OP_NO_COMPRESSION</code>
          is defined.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">add_certificate_authority</code> to process multiple certificates
          in a bundle.
        </li>
<li class="listitem">
          Eliminated deprecation warning with MSVC by using <code class="computeroutput">std::invoke_result</code>
          rather than <code class="computeroutput">std::result_of</code>.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">std::string_view</code> for C++17 or later, and <code class="computeroutput">std::experimental::string_view</code>
          for C++14. Define the preprocessor macro <code class="computeroutput">(BOOST_)ASIO_DISABLE_STD_STRING_VIEW</code>
          to force the use of std::experimental::string_view (assuming it is available)
          when compiling in C++17 mode.
        </li>
<li class="listitem">
          Ensured <code class="computeroutput">DynamicBuffer</code> template arguments are decayed before
          using in <code class="computeroutput">enable_if</code> tests.
        </li>
<li class="listitem">
          Changed documentation to distinguish legacy completion handlers (which
          are still required to be CopyConstructible) from new MoveConstructible
          handlers.
        </li>
<li class="listitem">
          Suppressed a discarded return value warning in the buffer debugging support.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">basic_yield_context</code> to work with completion signatures
          containing reference parameters.
        </li>
<li class="listitem">
          Ensured that stackful coroutines launched using <code class="computeroutput">spawn()</code> correctly
          store decayed copies of their function and handler arguments.
        </li>
<li class="listitem">
          Fixed some compatibility issues with Android.
        </li>
<li class="listitem">
          Fixed some minor portability issues in examples.
        </li>
</ul></div>
<h4>
<a name="asio.history.h2"></a>
      <span><a name="asio.history.asio_1_12_0"></a></span><a class="link" href="history.html#asio.history.asio_1_12_0">Asio
      1.12.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Completed the interface changes to reflect the Networking TS (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4656.pdf" target="_top">N4656</a>).
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                See the <a class="link" href="net_ts.html" title="Networking TS compatibility">list</a> of new interfaces
                and, where applicable, the corresponding old interfaces that have
                been superseded.
              </li>
<li class="listitem">
                The service template parameters, and the corresponding classes, are
                disabled by default. For example, instead of <code class="computeroutput">basic_socket&lt;Protocol,
                SocketService&gt;</code> we now have simply <code class="computeroutput">basic_socket&lt;Protocol&gt;</code>.
                The old interface can be enabled by defining the <code class="computeroutput">(BOOST_)ASIO_ENABLE_OLD_SERVICES</code>
                macro.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added support for customised handler tracking.
        </li>
<li class="listitem">
          Added reactor-related (i.e. descriptor readiness) events to handler tracking.
        </li>
<li class="listitem">
          Added special <a class="link" href="overview/core/concurrency_hint.html" title="Concurrency Hints">concurrency
          hint</a> values that may be used to disable locking on a per <code class="computeroutput">io_context</code>
          basis.
        </li>
<li class="listitem">
          Enabled perfect forwarding for the first <code class="computeroutput">ssl::stream&lt;&gt;</code>
          constructor argument.
        </li>
<li class="listitem">
          Added ability to release ownership of the underlying native socket. (Requires
          Windows 8.1 or later when using the I/O completion port backend.)
        </li>
</ul></div>
<h4>
<a name="asio.history.h3"></a>
      <span><a name="asio.history.asio_1_11_0"></a></span><a class="link" href="history.html#asio.history.asio_1_11_0">Asio
      1.11.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implemented changes to substantially reflect the Networking Library Proposal
          (<a href="../www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4370.html" target="_top">N4370</a>).
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                New <code class="computeroutput">Executor</code> type requirements and classes to support
                an executor framework, including the <code class="computeroutput">execution_context</code>
                base class, the <code class="computeroutput">executor_work</code> class for tracking outstanding
                work, and the <code class="computeroutput">executor</code> polymorphic wrapper. Free functions
                <code class="computeroutput">dispatch()</code>, <code class="computeroutput">post()</code> and <code class="computeroutput">defer()</code>
                have been added and are used to submit function objects to executors.
              </li>
<li class="listitem">
                Completion handlers now have an associated executor and associated
                allocator. The free function <code class="computeroutput">wrap()</code> is used to associate
                an executor with a handler or other object. The handler hooks for
                allocation, invocation and continuation have been deprecated.
              </li>
<li class="listitem">
                A <code class="computeroutput">system_executor</code> class has been added as a default
                executor.
              </li>
<li class="listitem">
                The <code class="computeroutput">io_service</code> class is now derived from <code class="computeroutput">execution_context</code>
                and implements the executor type requirements in its nested <code class="computeroutput">executor_type</code>
                class. The member functions <code class="computeroutput">dispatch()</code>, <code class="computeroutput">post()</code>,
                <code class="computeroutput">defer()</code> and <code class="computeroutput">wrap()</code> have been deprecated.
                The <code class="computeroutput">io_service::work</code> class has been deprecated.
              </li>
<li class="listitem">
                The <code class="computeroutput">io_service</code> member function <code class="computeroutput">reset()</code>
                has been renamed to <code class="computeroutput">restart()</code>. The old name is retained
                for backward compatibility but has been deprecated.
              </li>
<li class="listitem">
                The <code class="computeroutput">make_service&lt;&gt;()</code> function is now used to add
                a new service to an execution context such as an <code class="computeroutput">io_service</code>.
                The <code class="computeroutput">add_service()</code> function has been deprecated.
              </li>
<li class="listitem">
                A new <code class="computeroutput">strand&lt;&gt;</code> template has been added to allow
                strand functionality to be used with generic executor types.
              </li>
<li class="listitem">
                I/O objects (such as sockets and timers) now provide access to their
                associated <code class="computeroutput">io_service</code> via a <code class="computeroutput">context()</code> member
                function. The <code class="computeroutput">get_io_service()</code> member function is deprecated.
              </li>
<li class="listitem">
                All asynchronous operations and executor operations now support move-only
                handlers. However, the deprecated <code class="computeroutput">io_service::post()</code>,
                <code class="computeroutput">io_service::dispatch()</code>, <code class="computeroutput">io_service::strand::post()</code>
                and <code class="computeroutput">io_service::strand::dispatch()</code> functions still require
                copyable handlers.
              </li>
<li class="listitem">
                Waitable timer objects are now movable.
              </li>
<li class="listitem">
                Waitable timers, socket iostreams and socket streambufs now provide
                an <code class="computeroutput">expiry()</code> member function for obtaining the expiry
                time. The accessors <code class="computeroutput">expires_at()</code> and <code class="computeroutput">expires_after()</code>
                have been deprecated, though those names are retained for the mutating
                members.
              </li>
<li class="listitem">
                The <code class="computeroutput">std::packaged_task</code> class template is now supported
                as a completion handler. The initiating operation automatically returns
                the future associated with the task. The <code class="computeroutput">package()</code> function
                has been added as a convenient factory for packaged tasks.
              </li>
<li class="listitem">
                Sockets, socket acceptors and descriptors now provide <code class="computeroutput">wait()</code>
                and <code class="computeroutput">async_wait()</code> operations that may be used to wait
                for readiness. The <code class="computeroutput">null_buffers</code> type has been deprecated.
              </li>
<li class="listitem">
                The proposed error code enum classes are simulated using namespaces.
                Existing asio error codes now have a correspondence with the standard
                error conditions.
              </li>
<li class="listitem">
                Conversion between IP address types, and conversion from string to
                address, is now supported via the <code class="computeroutput">address_cast&lt;&gt;()</code>,
                <code class="computeroutput">make_address()</code>, <code class="computeroutput">make_address_v4()</code> and
                <code class="computeroutput">make_address_v6()</code> free functions. The <code class="computeroutput">from_string()</code>,
                <code class="computeroutput">to_v4()</code>, <code class="computeroutput">to_v6()</code> and <code class="computeroutput">v4_mapped()</code>
                member functions have been deprecated.
              </li>
<li class="listitem">
                A default-constructed <code class="computeroutput">ip::address</code> now represents an
                invalid address value that is neither IPv4 nor IPv6.
              </li>
<li class="listitem">
                New <code class="computeroutput">buffer()</code> overloads that generate mutable buffers
                for non-const <code class="computeroutput">string</code> objects.
              </li>
<li class="listitem">
                Support for dynamic buffer sequences that automatically grow and
                shrink to accomodate data as it is read or written. This is a generic
                facility similar to the existing <code class="computeroutput">asio::streambuf</code> class.
                This support includes:
                <div class="itemizedlist"><ul class="itemizedlist" type="square">
<li class="listitem">
                      New <code class="computeroutput">dynamic_string_buffer</code> and <code class="computeroutput">dynamic_vector_buffer</code>
                      adapter classes that meet the <code class="computeroutput">DynamicBufferSequence</code>
                      type requirements.
                    </li>
<li class="listitem">
                      New <code class="computeroutput">dynamic_buffer()</code> factory functions for creating
                      a dynamic buffer adapter for a <code class="computeroutput">vector</code> or <code class="computeroutput">string</code>.
                    </li>
<li class="listitem">
                      New overloads for the <code class="computeroutput">read()</code>, <code class="computeroutput">async_read()</code>,
                      <code class="computeroutput">write()</code> and <code class="computeroutput">async_write()</code>, <code class="computeroutput">read_until()</code>
                      and <code class="computeroutput">async_read_until()</code> free functions that directly
                      support dynamic buffer sequences.
                    </li>
</ul></div>
              </li>
<li class="listitem">
                Support for networks and address ranges. Thanks go to Oliver Kowalke
                for contributing to the design and providing the implementation on
                which this facility is based. The following new classes have been
                added:
                <div class="itemizedlist"><ul class="itemizedlist" type="square">
<li class="listitem">
                      <code class="computeroutput">address_iterator_v4</code> for iterating across IPv4
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">address_iterator_v6</code> for iterating across IPv6
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">address_range_v4</code> to represent a range of IPv4
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">address_range_v6</code> to represent a range of IPv6
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">network_v4</code> for manipulating IPv4 CIDR addresses,
                      e.g. 1.2.3.0/24
                    </li>
<li class="listitem">
                      <code class="computeroutput">network_v6</code> for manipulating IPv6 CIDR addresses,
                      e.g. ffe0:/120
                    </li>
</ul></div>
              </li>
<li class="listitem">
                New convenience headers in <code class="literal">&lt;asio/ts/*.hpp&gt;</code>
                that correspond to the headers in the proposal.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new, executor-aware <code class="computeroutput">thread_pool</code> class.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">spawn()</code> to be executor-aware.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">spawn()</code> overload that takes only a function object.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">spawn()</code> and <code class="computeroutput">yield_context</code> to permit nested
          calls to the completion handler.
        </li>
<li class="listitem">
          Removed previously deprecated functions.
        </li>
<li class="listitem">
          Added options for disabling TLS v1.1 and v1.2.
        </li>
<li class="listitem">
          Changed the SSL wrapper to call the password callback when loading an in-memory
          key.
        </li>
<li class="listitem">
          Changed the tutorial to use <code class="computeroutput">std::endl</code> to ensure output is
          flushed.
        </li>
<li class="listitem">
          Fixed false SSL error reports by ensuring that the SSL error queue is cleared
          prior to each operation.
        </li>
<li class="listitem">
          Fixed an <code class="computeroutput">ssl::stream&lt;&gt;</code> bug that may result in spurious
          'short read' errors.
        </li>
<li class="listitem">
          Enabled perfect forwarding for the first <code class="computeroutput">ssl::stream&lt;&gt;</code>
          constructor argument.
        </li>
<li class="listitem">
          Added standalone Asio support for Clang when used with libstdc++ and C++11.
        </li>
<li class="listitem">
          Fixed an unsigned integer overflow reported by Clang's integer sanitizer.
        </li>
<li class="listitem">
          Added support for move-only return types when using a <code class="computeroutput">yield_context</code>
          object with asynchronous operations.
        </li>
<li class="listitem">
          Ensured errors generated by Windows' <code class="computeroutput">ConnectEx</code> function are
          mapped to their portable equivalents.
        </li>
<li class="listitem">
          Changed multicast test to treat certain <code class="computeroutput">join_group</code> failures
          as non-fatal.
        </li>
</ul></div>
<h4>
<a name="asio.history.h4"></a>
      <span><a name="asio.history.asio_1_10_5"></a></span><a class="link" href="history.html#asio.history.asio_1_10_5">Asio
      1.10.5</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed the <code class="literal">kqueue</code> reactor so that it works on FreeBSD.
        </li>
<li class="listitem">
          Fixed an issue in the <code class="literal">kqueue</code> reactor which resulted
          in spinning when using serial ports on Mac OS.
        </li>
<li class="listitem">
          Fixed <code class="literal">kqueue</code> reactor support for read-only file descriptors.
        </li>
<li class="listitem">
          Fixed a compile error when using the <code class="literal">/dev/poll</code> reactor.
        </li>
<li class="listitem">
          Changed the Windows backend to use <code class="computeroutput">WSASocketW</code>, as <code class="computeroutput">WSASocketA</code>
          has been deprecated.
        </li>
<li class="listitem">
          Fixed some warnings reported by Visual C++ 2013.
        </li>
<li class="listitem">
          Fixed integer type used in the WinRT version of the byte-order conversion
          functions.
        </li>
<li class="listitem">
          Changed documentation to indicate that <code class="computeroutput">use_future</code> and <code class="computeroutput">spawn()</code>
          are not made available when including the <code class="computeroutput">asio.hpp</code> convenience
          header.
        </li>
<li class="listitem">
          Explicitly marked <code class="computeroutput">asio::strand</code> as deprecated. Use <code class="computeroutput">asio::io_service::strand</code>
          instead.
        </li>
</ul></div>
<h4>
<a name="asio.history.h5"></a>
      <span><a name="asio.history.asio_1_10_4"></a></span><a class="link" href="history.html#asio.history.asio_1_10_4">Asio
      1.10.4</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Stopped using certain Winsock functions that are marked as deprecated in
          the latest Visual C++ and Windows SDK.
        </li>
<li class="listitem">
          Fixed a shadow variable warning on Windows.
        </li>
<li class="listitem">
          Fixed a regression in the <code class="literal">kqueue</code> backend that was introduced
          in Asio 1.10.2.
        </li>
<li class="listitem">
          Added a workaround for building the unit tests with <code class="literal">gcc</code>
          on AIX.
        </li>
</ul></div>
<h4>
<a name="asio.history.h6"></a>
      <span><a name="asio.history.asio_1_10_3"></a></span><a class="link" href="history.html#asio.history.asio_1_10_3">Asio
      1.10.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Worked around a <code class="literal">gcc</code> problem to do with anonymous enums.
        </li>
<li class="listitem">
          Reverted the Windows <code class="computeroutput">HANDLE</code> backend change to ignore <code class="computeroutput">ERROR_MORE_DATA</code>.
          Instead, the error will be propagated as with any other (i.e. in an <code class="computeroutput">error_code</code>
          or thrown as a <code class="computeroutput">system_error</code>), and the number of bytes transferred
          will be returned. For code that needs to handle partial messages, the
          <code class="computeroutput">error_code</code> overload should be used.
        </li>
<li class="listitem">
          Fixed an off-by-one error in the <code class="computeroutput">signal_set</code> implementation's
          signal number check.
        </li>
<li class="listitem">
          Changed the Windows IOCP backend to not assume that <code class="computeroutput">SO_UPDATE_CONNECT_CONTEXT</code>
          is defined.
        </li>
<li class="listitem">
          Fixed a Windows-specific issue, introduced in Asio 1.10.2, by using <code class="computeroutput">VerifyVersionInfo</code>
          rather than <code class="computeroutput">GetVersionEx</code>, as <code class="computeroutput">GetVersionEx</code> has
          been deprecated.
        </li>
<li class="listitem">
          Changed to use SSE2 intrinsics rather than inline assembly, to allow the
          Cray compiler to work.
        </li>
</ul></div>
<h4>
<a name="asio.history.h7"></a>
      <span><a name="asio.history.asio_1_10_2"></a></span><a class="link" href="history.html#asio.history.asio_1_10_2">Asio
      1.10.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed <code class="computeroutput">asio::spawn()</code> to work correctly with new Boost.Coroutine
          interface.
        </li>
<li class="listitem">
          Ensured that incomplete <code class="computeroutput">asio::spawn()</code> coroutines are correctly
          unwound when cleaned up by the <code class="computeroutput">io_service</code> destructor.
        </li>
<li class="listitem">
          Fixed delegation of continuation hook for handlers produced by <code class="computeroutput">io_service::wrap()</code>
          and <code class="computeroutput">strand::wrap()</code>.
        </li>
<li class="listitem">
          Changed the Windows I/O completion port backend to use <code class="computeroutput">ConnectEx</code>,
          if available, for connection-oriented IP sockets.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">io_service</code> backend for non-Windows (and non-IOCP
          Windows) platforms to use a single condition variable per <code class="computeroutput">io_service</code>
          instance. This addresses a potential race condition when <code class="computeroutput">run_one()</code>
          is used from multiple threads.
        </li>
<li class="listitem">
          Prevented integer overflow when computing timeouts based on some <code class="computeroutput">boost::chrono</code>
          and <code class="computeroutput">std::chrono</code> clocks.
        </li>
<li class="listitem">
          Made further changes to <code class="computeroutput">EV_CLEAR</code> handling in the kqueue backend,
          to address other cases where the <code class="computeroutput">close()</code> system call may hang
          on Mac OS X.
        </li>
<li class="listitem">
          Fixed infinite recursion in implementation of <code class="computeroutput">resolver_query_base::flags::operator~</code>.
        </li>
<li class="listitem">
          Made the <code class="computeroutput">select</code> reactor more efficient on Windows for large
          numbers of sockets.
        </li>
<li class="listitem">
          Fixed a Windows-specific type-aliasing issue reported by <code class="literal">gcc</code>.
        </li>
<li class="listitem">
          Prevented execution of compile-time-only buffer test to avoid triggering
          an address sanitiser warning.
        </li>
<li class="listitem">
          Disabled the <code class="computeroutput">GetQueuedCompletionStatus</code> timeout workaround
          on recent versions of Windows.
        </li>
<li class="listitem">
          Changed implementation for Windows Runtime to use <code class="computeroutput">FormatMessageW</code>
          rather than <code class="computeroutput">FormatMessageA</code>, as the Windows store does not
          permit the latter.
        </li>
<li class="listitem">
          Added support for string-based scope IDs when using link-local multicast
          addresses.
        </li>
<li class="listitem">
          Changed IPv6 multicast group join to use the address's scope ID as the
          interface, if an interface is not explicitly specified.
        </li>
<li class="listitem">
          Fixed multicast test failure on Mac OS X and the BSDs by using a link-local
          multicast address.
        </li>
<li class="listitem">
          Various minor documentation improvements.
        </li>
</ul></div>
<h4>
<a name="asio.history.h8"></a>
      <span><a name="asio.history.asio_1_10_1"></a></span><a class="link" href="history.html#asio.history.asio_1_10_1">Asio
      1.10.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implemented a limited port to Windows Runtime. This support requires that
          the language extensions be enabled. Due to the restricted facilities exposed
          by the Windows Runtime API, the port also comes with the following caveats:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                The core facilities such as the <code class="computeroutput">io_service</code>, <code class="computeroutput">strand</code>,
                buffers, composed operations, timers, etc., should all work as normal.
              </li>
<li class="listitem">
                For sockets, only client-side TCP is supported.
              </li>
<li class="listitem">
                Explicit binding of a client-side TCP socket is not supported.
              </li>
<li class="listitem">
                The <code class="computeroutput">cancel()</code> function is not supported for sockets.
                Asynchronous operations may only be cancelled by closing the socket.
              </li>
<li class="listitem">
                Operations that use <code class="computeroutput">null_buffers</code> are not supported.
              </li>
<li class="listitem">
                Only <code class="computeroutput">tcp::no_delay</code> and <code class="computeroutput">socket_base::keep_alive</code>
                options are supported.
              </li>
<li class="listitem">
                Resolvers do not support service names, only numbers. I.e. you must
                use "80" rather than "http".
              </li>
<li class="listitem">
                Most resolver query flags have no effect.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Extended the ability to use Asio without Boost to include Microsoft Visual
          Studio 2012. When using a C++11 compiler, most of Asio may now be used
          without a dependency on Boost header files or libraries. To use Asio in
          this way, define <code class="computeroutput">ASIO_STANDALONE</code> on your compiler command
          line or as part of the project options. This standalone configuration has
          been tested for the following platforms and compilers:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Microsoft Visual Studio 2012
              </li>
<li class="listitem">
                Linux with g++ 4.7 or 4.8 (requires <code class="literal">-std=c++11</code>)
              </li>
<li class="listitem">
                Mac OS X with clang++ / Xcode 4.6 (requires <code class="literal">-std=c++11 -stdlib=libc++</code>)
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a regression (introduced in 1.10.0) where, on some platforms, errors
          from <code class="computeroutput">async_connect</code> were not correctly propagated through to
          the completion handler.
        </li>
<li class="listitem">
          Fixed a Windows-specific regression (introduced in 1.10.0) that occurs
          when multiple threads are running an <code class="computeroutput">io_service</code>. When the
          bug occurs, the result of an asynchronous operation (error and bytes tranferred)
          is incorrectly discarded and zero values used instead. For TCP sockets
          this results in spurious end-of-file notifications.
        </li>
<li class="listitem">
          Fixed a bug in handler tracking, where it was not correctly printing out
          some handler IDs.
        </li>
<li class="listitem">
          Fixed the comparison used to test for successful synchronous accept operations
          so that it works correctly with unsigned socket descriptors.
        </li>
<li class="listitem">
          Ensured the signal number is correctly passed to the completion handler
          when starting an <code class="computeroutput">async_wait</code> on a signal that is already raised.
        </li>
<li class="listitem">
          Suppressed a g++ 4.8+ warning about unused typedefs.
        </li>
<li class="listitem">
          Enabled the move optimisation for handlers that use the default invocation
          hook.
        </li>
<li class="listitem">
          Clarified that programs must not issue overlapping <code class="computeroutput">async_write_at</code>
          operations.
        </li>
<li class="listitem">
          Changed the Windows <code class="computeroutput">HANDLE</code> backend to treat <code class="computeroutput">ERROR_MORE_DATA</code>
          as a non-fatal error when returned by <code class="computeroutput">GetOverlappedResult</code>
          for a synchronous read.
        </li>
<li class="listitem">
          Visual C++ language extensions use <code class="computeroutput">generic</code> as a keyword. Added
          a workaround that renames the namespace to <code class="computeroutput">cpp_generic</code> when
          those language extensions are in effect.
        </li>
<li class="listitem">
          Fixed some asynchronous operations that missed out on getting <code class="computeroutput">async_result</code>
          support in 1.10.0. In particular, the buffered stream templates have been
          updated so that they adhere to current handler patterns.
        </li>
<li class="listitem">
          Enabled move support for Microsoft Visual Studio 2012.
        </li>
<li class="listitem">
          Added <code class="computeroutput">use_future</code> support for Microsoft Visual Studio 2012.
        </li>
<li class="listitem">
          Removed a use of <code class="computeroutput">std::min</code> in the Windows IOCP backend to avoid
          a dependency on the <code class="computeroutput">&lt;algorithm&gt;</code> header.
        </li>
<li class="listitem">
          Eliminated some unnecessary handler copies.
        </li>
<li class="listitem">
          Fixed support for older versions of OpenSSL that do not provide the <code class="computeroutput">SSL_CTX_clear_options</code>
          function.
        </li>
<li class="listitem">
          Fixed various minor and cosmetic issues in code and documentation.
        </li>
</ul></div>
<h4>
<a name="asio.history.h9"></a>
      <span><a name="asio.history.asio_1_10_0"></a></span><a class="link" href="history.html#asio.history.asio_1_10_0">Asio
      1.10.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added new traits classes, <code class="computeroutput">handler_type</code> and <code class="computeroutput">async_result</code>,
          that allow the customisation of the return type of an initiating function.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">asio::spawn()</code> function, a high-level wrapper for
          running stackful coroutines, based on the Boost.Coroutine library. The
          <code class="computeroutput">spawn()</code> function enables programs to implement asynchronous
          logic in a synchronous manner. For example: <code class="computeroutput">size_t n = my_socket.async_read_some(my_buffer,
          yield);</code>. For further information, see <a class="link" href="overview/core/spawn.html" title="Stackful Coroutines">Stackful
          Coroutines</a>.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">asio::use_future</code> special value, which provides first-class
          support for returning a C++11 <code class="computeroutput">std::future</code> from an asynchronous
          operation's initiating function. For example: <code class="computeroutput">future&lt;size_t&gt;
          = my_socket.async_read_some(my_buffer, asio::use_future);</code>. For further
          information, see <a class="link" href="overview/cpp2011/futures.html" title="Futures">C++ 2011
          Support - Futures</a>.
        </li>
<li class="listitem">
          Promoted the stackless coroutine class and macros to be part of Asio's
          documented interface, rather than part of the HTTP server 4 example. For
          further information, see <a class="link" href="overview/core/coroutine.html" title="Stackless Coroutines">Stackless
          Coroutines</a>.
        </li>
<li class="listitem">
          Added a new handler hook called <code class="computeroutput">asio_handler_is_continuation</code>.
          Asynchronous operations may represent a continuation of the asynchronous
          control flow associated with the current executing handler. The <code class="computeroutput">asio_handler_is_continuation</code>
          hook can be customised to return <code class="computeroutput">true</code> if this is the case,
          and Asio's implementation can use this knowledge to optimise scheduling
          of the new handler. To cover common cases, Asio customises the hook for
          strands, <code class="computeroutput">spawn()</code> and composed asynchronous operations.
        </li>
<li class="listitem">
          Added four new generic protocol classes, <code class="computeroutput">generic::datagram_protocol</code>,
          <code class="computeroutput">generic::raw_protocol</code>, <code class="computeroutput">generic::seq_packet_protocol</code>
          and <code class="computeroutput">generic::stream_protocol</code>, which implement the <code class="computeroutput">Protocol</code>
          type requirements, but allow the user to specify the address family (e.g.
          <code class="computeroutput">AF_INET</code>) and protocol type (e.g. <code class="computeroutput">IPPROTO_TCP</code>)
          at runtime. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Added C++11 move constructors that allow the conversion of a socket (or
          acceptor) into a more generic type. For example, an <code class="computeroutput">ip::tcp::socket</code>
          can be converted into a <code class="computeroutput">generic::stream_protocol::socket</code> via
          move construction. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Extended the <code class="computeroutput">basic_socket_acceptor&lt;&gt;</code>'s <code class="computeroutput">accept()</code>
          and <code class="computeroutput">async_accept()</code> functions to allow a new connection to
          be accepted directly into a socket of a more generic type. For example,
          an <code class="computeroutput">ip::tcp::acceptor</code> can be used to accept into a <code class="computeroutput">generic::stream_protocol::socket</code>
          object. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Moved existing examples into a C++03-specific directory, and added a new
          directory for C++11-specific examples. A limited subset of the C++03 examples
          have been converted to their C++11 equivalents.
        </li>
<li class="listitem">
          Add the ability to use Asio without Boost, for a limited set of platforms.
          When using a C++11 compiler, most of Asio may now be used without a dependency
          on Boost header files or libraries. To use Asio in this way, define <code class="computeroutput">ASIO_STANDALONE</code>
          on your compiler command line or as part of the project options. This standalone
          configuration has currently been tested for the following platforms and
          compilers:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Linux with g++ 4.7 (requires <code class="literal">-std=c++11</code>)
              </li>
<li class="listitem">
                Mac OS X with clang++ / Xcode 4.6 (requires <code class="literal">-std=c++11 -stdlib=libc++</code>)
              </li>
</ul></div>
        </li>
<li class="listitem">
          Various SSL enhancements. Thanks go to Nick Jones, on whose work these
          changes are based.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Added support for SSL handshakes with re-use of data already read
                from the wire. New overloads of the <code class="computeroutput">ssl::stream&lt;&gt;</code>
                class's <code class="computeroutput">handshake()</code> and <code class="computeroutput">async_handshake()</code>
                functions have been added. These accept a <code class="computeroutput">ConstBufferSequence</code>
                to be used as initial input to the ssl engine for the handshake procedure.
              </li>
<li class="listitem">
                Added support for creation of TLSv1.1 and TLSv1.2 <code class="computeroutput">ssl::context</code>
                objects.
              </li>
<li class="listitem">
                Added a <code class="computeroutput">set_verify_depth()</code> function to the <code class="computeroutput">ssl::context</code>
                and <code class="computeroutput">ssl::stream&lt;&gt;</code> classes.
              </li>
<li class="listitem">
                Added the ability to load SSL certificate and key data from memory
                buffers. New functions, <code class="computeroutput">add_certificate_authority()</code>,
                <code class="computeroutput">use_certificate()</code>, <code class="computeroutput">use_certificate_chain()</code>,
                <code class="computeroutput">use_private_key()</code>, <code class="computeroutput">use_rsa_private_key()</code>
                and <code class="computeroutput">use_tmp_dh()</code>, have been added to the <code class="computeroutput">ssl::context</code>
                class.
              </li>
<li class="listitem">
                Changed <code class="computeroutput">ssl::context</code> to automatically disable SSL compression
                by default. To enable, use the new <code class="computeroutput">ssl::context::clear_options()</code>
                function, as in <code class="computeroutput">my_context.clear_options(ssl::context::no_compression)</code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a potential deadlock in <code class="computeroutput">signal_set</code> implementation.
        </li>
<li class="listitem">
          Fixed an error in acceptor example in documentation.
        </li>
<li class="listitem">
          Fixed copy-paste errors in waitable timer documentation.
        </li>
<li class="listitem">
          Added assertions to satisfy some code analysis tools.
        </li>
<li class="listitem">
          Fixed a malformed <code class="computeroutput">#warning</code> directive.
        </li>
<li class="listitem">
          Fixed a potential data race in the Linux <code class="computeroutput">epoll</code> implementation.
        </li>
<li class="listitem">
          Fixed a Windows-specific bug, where certain operations might generate an
          <code class="computeroutput">error_code</code> with an invalid (i.e. <code class="computeroutput">NULL</code>) <code class="computeroutput">error_category</code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">basic_waitable_timer</code>'s underlying implementation so
          that it can handle any <code class="computeroutput">time_point</code> value without overflowing
          the intermediate duration objects.
        </li>
<li class="listitem">
          Fixed a problem with lost thread wakeups that can occur when making concurrent
          calls to <code class="computeroutput">run()</code> and <code class="computeroutput">poll()</code> on the same <code class="computeroutput">io_service</code>
          object.
        </li>
<li class="listitem">
          Fixed implementation of asynchronous connect operation so that it can cope
          with spurious readiness notifications from the reactor.
        </li>
<li class="listitem">
          Fixed a memory leak in the <code class="computeroutput">ssl::rfc2818_verification</code> class.
        </li>
<li class="listitem">
          Added a mechanism for disabling automatic Winsock initialisation. See the
          header file <code class="literal">asio/detail/winsock_init.hpp</code> for details.
        </li>
</ul></div>
<h4>
<a name="asio.history.h10"></a>
      <span><a name="asio.history.asio_1_8_3"></a></span><a class="link" href="history.html#asio.history.asio_1_8_3">Asio
      1.8.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed some 64-to-32-bit conversion warnings.
        </li>
<li class="listitem">
          Fixed various small errors in documentation and comments.
        </li>
<li class="listitem">
          Fixed an error in the example embedded in <code class="computeroutput">basic_socket::get_option</code>'s
          documentation.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">long</code> rather than <code class="computeroutput">int</code> for SSL_CTX
          options, to match OpenSSL.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">_snwprintf</code> to address a compile error due to
          the changed <code class="computeroutput">swprintf</code> signature in recent versions of MinGW.
        </li>
<li class="listitem">
          Fixed a deadlock that can occur on Windows when shutting down a pool of
          <code class="computeroutput">io_service</code> threads due to running out of work.
        </li>
<li class="listitem">
          Changed UNIX domain socket example to treat errors from <code class="computeroutput">accept</code>
          as non-fatal.
        </li>
<li class="listitem">
          Added a small block recycling optimisation to improve default memory allocation
          behaviour.
        </li>
</ul></div>
<h4>
<a name="asio.history.h11"></a>
      <span><a name="asio.history.asio_1_8_2"></a></span><a class="link" href="history.html#asio.history.asio_1_8_2">Asio
      1.8.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed an incompatibility between <code class="computeroutput">ip::tcp::iostream</code> and C++11.
        </li>
<li class="listitem">
          Decorated GCC attribute names with underscores to prevent interaction with
          user-defined macros.
        </li>
<li class="listitem">
          Added missing <code class="computeroutput">#include &lt;cctype&gt;</code>, needed for some versions
          of MinGW.
        </li>
<li class="listitem">
          Changed to use <code class="literal">gcc</code>'s atomic builtins on ARM CPUs, when
          available.
        </li>
<li class="listitem">
          Changed strand destruction to be a no-op, to allow strand objects to be
          destroyed after their associated <code class="computeroutput">io_service</code> has been destroyed.
        </li>
<li class="listitem">
          Added support for some newer versions of glibc which provide the <code class="computeroutput">epoll_create1()</code>
          function but always fail with ENOSYS.
        </li>
<li class="listitem">
          Changed the SSL implementation to throw an exception if SSL engine initialisation
          fails.
        </li>
<li class="listitem">
          Fixed another regression in <code class="computeroutput">buffered_write_stream</code>.
        </li>
<li class="listitem">
          Implemented various minor performance improvements, primarily targeted
          at Linux x86 and x86-64 platforms.
        </li>
</ul></div>
<h4>
<a name="asio.history.h12"></a>
      <span><a name="asio.history.asio_1_8_1"></a></span><a class="link" href="history.html#asio.history.asio_1_8_1">Asio
      1.8.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Changed the <code class="computeroutput">epoll_reactor</code> backend to do lazy registration
          for <code class="computeroutput">EPOLLOUT</code> events.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput">epoll_reactor</code> handling of out-of-band data, which
          was broken by an incomplete fix in the last release.
        </li>
<li class="listitem">
          Changed Asio's SSL wrapper to respect OpenSSL's <code class="computeroutput">OPENSSL_NO_ENGINE</code>
          feature test <code class="computeroutput">#define</code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">windows::object_handle</code> so that it works with Windows
          compilers that support C++11 move semantics (such as <code class="literal">g++</code>).
        </li>
<li class="listitem">
          Improved the performance of strand rescheduling.
        </li>
<li class="listitem">
          Added support for <code class="literal">g++</code> 4.7 when compiling in C++11 mode.
        </li>
<li class="listitem">
          Fixed a problem where <code class="computeroutput">signal_set</code> handlers were not being delivered
          when the <code class="computeroutput">io_service</code> was constructed with a <code class="computeroutput">concurrency_hint</code>
          of 1.
        </li>
</ul></div>
<h4>
<a name="asio.history.h13"></a>
      <span><a name="asio.history.asio_1_8_0"></a></span><a class="link" href="history.html#asio.history.asio_1_8_0">Asio
      1.8.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new class template <code class="computeroutput">basic_waitable_timer</code> based around
          the C++11 clock type requirements. It may be used with the clocks from
          the C++11 <code class="computeroutput">&lt;chrono&gt;</code> library facility or, if those are
          not available, Boost.Chrono. The typedefs <code class="computeroutput">high_resolution_timer</code>,
          <code class="computeroutput">steady_timer</code> and <code class="computeroutput">system_timer</code> may be used to
          create timer objects for the standard clock types.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">windows::object_handle</code> class for performing waits
          on Windows kernel objects. Thanks go to Boris Schaeling for contributing
          substantially to the development of this feature.
        </li>
<li class="listitem">
          On Linux, <code class="computeroutput">connect()</code> can return EAGAIN in certain circumstances.
          Remapped this to another error so that it doesn't look like a non-blocking
          operation.
        </li>
<li class="listitem">
          Fixed a compile error on NetBSD.
        </li>
<li class="listitem">
          Fixed deadlock on Mac OS X.
        </li>
<li class="listitem">
          Fixed a regression in <code class="computeroutput">buffered_write_stream</code>.
        </li>
<li class="listitem">
          Fixed a non-paged pool "leak" on Windows when an <code class="computeroutput">io_service</code>
          is repeatedly run without anything to do.
        </li>
<li class="listitem">
          Reverted earlier change to allow some speculative operations to be performed
          without holding the lock, as it introduced a race condition in some multithreaded
          scenarios.
        </li>
<li class="listitem">
          Fixed a bug where the second buffer in an array of two buffers may be ignored
          if the first buffer is empty.
        </li>
</ul></div>
<h4>
<a name="asio.history.h14"></a>
      <span><a name="asio.history.asio_1_6_1"></a></span><a class="link" href="history.html#asio.history.asio_1_6_1">Asio
      1.6.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implemented various performance improvements, including:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Using thread-local operation queues in single-threaded use cases
                (i.e. when <code class="computeroutput">concurrency_hint</code> is 1) to eliminate a lock/unlock
                pair.
              </li>
<li class="listitem">
                Allowing some <code class="computeroutput">epoll_reactor</code> speculative operations to
                be performed without holding the lock.
              </li>
<li class="listitem">
                Improving locality of reference by performing an <code class="computeroutput">epoll_reactor</code>'s
                I/O operation immediately before the corresponding handler is called.
                This also improves scalability across CPUs when multiple threads
                are running the <code class="computeroutput">io_service</code>.
              </li>
<li class="listitem">
                Specialising asynchronous read and write operations for buffer sequences
                that are arrays (<code class="computeroutput">boost::array</code> or <code class="computeroutput">std::array</code>)
                of exactly two buffers.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a compile error in the regex overload of <code class="computeroutput">async_read_until</code>.
        </li>
<li class="listitem">
          Fixed a Windows-specific compile error by explicitly specifying the <code class="computeroutput">signal()</code>
          function from the global namespace.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">deadline_timer</code> implementation so that it does
          not read the clock unless the timer heap is non-empty.
        </li>
<li class="listitem">
          Changed the SSL stream's buffers' sizes so that they are large enough to
          hold a complete TLS record.
        </li>
<li class="listitem">
          Fixed the behaviour of the synchronous <code class="computeroutput">null_buffers</code> operations
          so that they obey the user's non-blocking setting.
        </li>
<li class="listitem">
          Changed to set the size of the select <code class="computeroutput">fd_set</code> at runtime when
          using Windows.
        </li>
<li class="listitem">
          Disabled an MSVC warning due to const qualifier being applied to function
          type.
        </li>
<li class="listitem">
          Fixed a crash that occurs when using the Intel C++ compiler.
        </li>
<li class="listitem">
          Changed the initialisation of the OpenSSL library so that it supports all
          available algorithms.
        </li>
<li class="listitem">
          Fixed the SSL error mapping used when the session is gracefully shut down.
        </li>
<li class="listitem">
          Added some latency test programs.
        </li>
<li class="listitem">
          Clarified that a read operation ends when the buffer is full.
        </li>
<li class="listitem">
          Fixed an exception safety issue in <code class="computeroutput">epoll_reactor</code> initialisation.
        </li>
<li class="listitem">
          Made the number of strand implementations configurable by defining <code class="computeroutput">(BOOST_)ASIO_STRAND_IMPLEMENTATIONS</code>
          to the desired number.
        </li>
<li class="listitem">
          Added support for a new <code class="computeroutput">(BOOST_)ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION</code>
          flag which switches the allocation of strand implementations to use a round-robin
          approach rather than hashing.
        </li>
<li class="listitem">
          Fixed potential strand starvation issue that can occur when <code class="computeroutput">strand.post()</code>
          is used.
        </li>
</ul></div>
<h4>
<a name="asio.history.h15"></a>
      <span><a name="asio.history.asio_1_6_0"></a></span><a class="link" href="history.html#asio.history.asio_1_6_0">Asio
      1.6.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved support for C++0x move construction to further reduce copying
          of handler objects. In certain designs it is possible to eliminate virtually
          all copies. Move support is now enabled when compiling in <code class="literal">-std=c++0x</code>
          mode on g++ 4.5 or higher.
        </li>
<li class="listitem">
          Added build support for platforms that don't provide either of <code class="computeroutput">signal()</code>
          or <code class="computeroutput">sigaction()</code>.
        </li>
<li class="listitem">
          Changed to use C++0x variadic templates when they are available, rather
          than generating function overloads using the Boost.Preprocessor library.
        </li>
<li class="listitem">
          Ensured the value of <code class="computeroutput">errno</code> is preserved across the implementation's
          signal handler.
        </li>
<li class="listitem">
          On Windows, ensured the count of outstanding work is decremented for abandoned
          operations (i.e. operations that are being cleaned up within the <code class="computeroutput">io_service</code>
          destructor).
        </li>
<li class="listitem">
          Fixed behaviour of zero-length reads and writes in the new SSL implementation.
        </li>
<li class="listitem">
          Added support for building with OpenSSL 1.0 when <code class="computeroutput">OPENSSL_NO_SSL2</code>
          is defined.
        </li>
<li class="listitem">
          Changed most examples to treat a failure by an accept operation as non-fatal.
        </li>
<li class="listitem">
          Fixed an error in the <code class="literal">tick_count_timer</code> example by making
          the duration type signed. Previously, a wait on an already-passed deadline
          would not return for a very long time.
        </li>
</ul></div>
<h4>
<a name="asio.history.h16"></a>
      <span><a name="asio.history.asio_1_5_3"></a></span><a class="link" href="history.html#asio.history.asio_1_5_3">Asio
      1.5.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new, completely rewritten SSL implementation. The new implementation
          compiles faster, shows substantially improved performance, and supports
          custom memory allocation and handler invocation. It includes new API features
          such as certificate verification callbacks and has improved error reporting.
          The new implementation is source-compatible with the old for most uses.
          However, if necessary, the old implementation may still be used by defining
          <code class="computeroutput">(BOOST_)ASIO_ENABLE_OLD_SSL</code>.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">asio::buffer()</code> overloads for <code class="computeroutput">std::array</code>,
          when available. The support is automatically enabled when compiling in
          <code class="literal">-std=c++0x</code> mode on g++ 4.3 or higher, or when using
          MSVC 10. The support may be explicitly enabled by defining <code class="computeroutput">(BOOST_)ASIO_HAS_STD_ARRAY</code>,
          or disabled by defining <code class="computeroutput">(BOOST_)ASIO_DISABLE_STD_ARRAY</code>.
        </li>
<li class="listitem">
          Changed to use the C++0x standard library templates <code class="computeroutput">array</code>,
          <code class="computeroutput">shared_ptr</code>, <code class="computeroutput">weak_ptr</code> and <code class="computeroutput">atomic</code>
          when they are available, rather than the Boost equivalents.
        </li>
<li class="listitem">
          Support for <code class="computeroutput">std::error_code</code> and <code class="computeroutput">std::system_error</code>
          is no longer enabled by default for g++ 4.5, as that compiler's standard
          library does not implement <code class="computeroutput">std::system_error::what()</code> correctly.
        </li>
</ul></div>
<h4>
<a name="asio.history.h17"></a>
      <span><a name="asio.history.asio_1_5_2"></a></span><a class="link" href="history.html#asio.history.asio_1_5_2">Asio
      1.5.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for C++0x move construction and assignment to sockets, serial
          ports, POSIX descriptors and Windows handles.
        </li>
<li class="listitem">
          Added support for the <code class="computeroutput">fork()</code> system call. Programs that use
          <code class="computeroutput">fork()</code> must call <code class="computeroutput">io_service.notify_fork()</code> at
          the appropriate times. Two new examples have been added showing how to
          use this feature.
        </li>
<li class="listitem">
          Cleaned up the handling of errors reported by the <code class="computeroutput">close()</code>
          system call. In particular, assume that most operating systems won't have
          <code class="computeroutput">close()</code> fail with <code class="computeroutput">EWOULDBLOCK</code>, but if it does
          then set the blocking mode and restart the call. If any other error occurs,
          assume the descriptor is closed.
        </li>
<li class="listitem">
          The kqueue flag <code class="computeroutput">EV_ONESHOT</code> seems to cause problems on some
          versions of Mac OS X, with the <code class="computeroutput">io_service</code> destructor getting
          stuck inside the <code class="computeroutput">close()</code> system call. Changed the kqueue backend
          to use <code class="computeroutput">EV_CLEAR</code> instead.
        </li>
<li class="listitem">
          Changed exception reporting to include the function name in exception
          <code class="computeroutput">what()</code> messages.
        </li>
<li class="listitem">
          Fixed an insufficient initialisers warning with MinGW.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">shutdown_service()</code> member functions to be private.
        </li>
<li class="listitem">
          Added archetypes for testing socket option functions.
        </li>
<li class="listitem">
          Added a missing lock in <code class="computeroutput">signal_set_service::cancel()</code>.
        </li>
<li class="listitem">
          Fixed a copy/paste error in <code class="computeroutput">SignalHandler</code> example.
        </li>
<li class="listitem">
          Added the inclusion of the signal header to <code class="computeroutput">signal_set_service.hpp</code>
          so that constants like <code class="computeroutput">NSIG</code> may be used.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">signal_set_service</code> implementation so that it doesn't
          assume that <code class="computeroutput">SIGRTMAX</code> is a compile-time constant.
        </li>
<li class="listitem">
          Changed the Boost.Asio examples so that they don't use Boost.Thread's convenience
          header. Use the header file that is specifically for the boost::thread
          class instead.
        </li>
</ul></div>
<h4>
<a name="asio.history.h18"></a>
      <span><a name="asio.history.asio_1_5_1"></a></span><a class="link" href="history.html#asio.history.asio_1_5_1">Asio
      1.5.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for signal handling, using a new class called <code class="computeroutput">signal_set</code>.
          Programs may add one or more signals to the set, and then perform an <code class="computeroutput">async_wait()</code>
          operation. The specified handler will be called when one of the signals
          occurs. The same signal number may registered with multiple <code class="computeroutput">signal_set</code>
          objects, however the signal number must be used only with Asio.
        </li>
<li class="listitem">
          Added handler tracking, a new debugging aid. When enabled by defining
          <code class="computeroutput">(BOOST_)ASIO_ENABLE_HANDLER_TRACKING</code>, Asio writes debugging
          output to the standard error stream. The output records asynchronous operations
          and the relationships between their handlers. It may be post-processed
          using the included <code class="literal">handlerviz.pl</code> tool to create a visual
          representation of the handlers (requires GraphViz).
        </li>
<li class="listitem">
          Fixed a bug in <code class="computeroutput">asio::streambuf</code> where the <code class="computeroutput">consume()</code>
          function did not always update the internal buffer pointers correctly.
          The problem may occur when the <code class="computeroutput">asio::streambuf</code> is filled with
          data using the standard C++ member functions such as <code class="computeroutput">sputn()</code>.
          (Note: the problem does not manifest when the streambuf is populated by
          the Asio free functions <code class="computeroutput">read()</code>, <code class="computeroutput">async_read()</code>,
          <code class="computeroutput">read_until()</code> or <code class="computeroutput">async_read_until()</code>.)
        </li>
<li class="listitem">
          Fixed a bug on kqueue-based platforms, where reactor read operations that
          return false from their <code class="computeroutput">perform()</code> function are not correctly
          re-registered with kqueue.
        </li>
<li class="listitem">
          Support for <code class="computeroutput">std::error_code</code> and <code class="computeroutput">std::system_error</code>
          is no longer enabled by default for MSVC10, as that compiler's standard
          library does not implement <code class="computeroutput">std::system_error::what()</code> correctly.
        </li>
<li class="listitem">
          Modified the <code class="computeroutput">buffers_iterator&lt;&gt;</code> and <code class="computeroutput">ip::basic_resolver_iterator</code>
          classes so that the value_type typedefs are non-const byte types.
        </li>
</ul></div>
<h4>
<a name="asio.history.h19"></a>
      <span><a name="asio.history.asio_1_5_0"></a></span><a class="link" href="history.html#asio.history.asio_1_5_0">Asio
      1.5.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for timeouts on socket iostreams, such as <code class="computeroutput">ip::tcp::iostream</code>.
          A timeout is set by calling <code class="computeroutput">expires_at()</code> or <code class="computeroutput">expires_from_now()</code>
          to establish a deadline. Any socket operations which occur past the deadline
          will put the iostream into a bad state.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">error()</code> member function to socket iostreams, for
          retrieving the error code from the most recent system call.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">basic_deadline_timer::cancel_one()</code> function. This
          function lets you cancel a single waiting handler on a timer. Handlers
          are cancelled in FIFO order.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">transfer_exactly()</code> completion condition. This
          can be used to send or receive a specified number of bytes even if the
          total size of the buffer (or buffer sequence) is larger.
        </li>
<li class="listitem">
          Added new free functions <code class="computeroutput">connect()</code> and <code class="computeroutput">async_connect()</code>.
          These operations try each endpoint in a list until the socket is successfully
          connected.
        </li>
<li class="listitem">
          Extended the <code class="computeroutput">buffer_size()</code> function so that it works for buffer
          sequences in addition to individual buffers.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">buffer_copy()</code> function that can be used to copy
          the raw bytes between individual buffers and buffer sequences.
        </li>
<li class="listitem">
          Added new non-throwing overloads of <code class="computeroutput">read()</code>, <code class="computeroutput">read_at()</code>,
          <code class="computeroutput">write()</code> and <code class="computeroutput">write_at()</code> that do not require a
          completion condition.
        </li>
<li class="listitem">
          Added friendlier compiler errors for when a completion handler does not
          meet the necessary type requirements. When C++0x is available (currently
          supported for g++ 4.5 or later, and MSVC 10), <code class="computeroutput">static_assert</code>
          is also used to generate an informative error message. This checking may
          be disabled by defining <code class="computeroutput">(BOOST_)ASIO_DISABLE_HANDLER_TYPE_REQUIREMENTS</code>.
        </li>
<li class="listitem">
          Added support for using <code class="computeroutput">std::error_code</code> and <code class="computeroutput">std::system_error</code>,
          when available. The support is automatically enabled when compiling in
          <code class="literal">-std=c++0x</code> mode on g++ 4.5 or higher, or when using
          MSVC 10. The support may be explicitly enabled by defining <code class="computeroutput">ASIO_HAS_STD_SYSTEM_ERROR</code>,
          or disabled by defining <code class="computeroutput">ASIO_DISABLE_STD_SYSTEM_ERROR</code>. (Available
          in non-Boost version of Asio only.)
        </li>
<li class="listitem">
          Made the <code class="computeroutput">is_loopback()</code>, <code class="computeroutput">is_unspecified()</code> and
          <code class="computeroutput">is_multicast()</code> functions consistently available across the
          <code class="computeroutput">ip::address</code>, <code class="computeroutput">ip::address_v4</code> and <code class="computeroutput">ip::address_v6</code>
          classes.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">non_blocking()</code> functions for managing the non-blocking
          behaviour of a socket or descriptor. The <code class="computeroutput">io_control()</code> commands
          named <code class="computeroutput">non_blocking_io</code> are now deprecated in favour of these
          new functions.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">native_non_blocking()</code> functions for managing the
          non-blocking mode of the underlying socket or descriptor. These functions
          are intended to allow the encapsulation of arbitrary non-blocking system
          calls as asynchronous operations, in a way that is transparent to the user
          of the socket object. The functions have no effect on the behaviour of
          the synchronous operations of the socket or descriptor.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">io_control()</code> member function for socket acceptors.
        </li>
<li class="listitem">
          For consistency with the C++0x standard library, deprecated the <code class="computeroutput">native_type</code>
          typedefs in favour of <code class="computeroutput">native_handle_type</code>, and the <code class="computeroutput">native()</code>
          member functions in favour of <code class="computeroutput">native_handle()</code>.
        </li>
<li class="listitem">
          Added a <code class="computeroutput">release()</code> member function to posix descriptors. This
          function releases ownership of the underlying native descriptor to the
          caller.
        </li>
<li class="listitem">
          Added support for sequenced packet sockets (<code class="computeroutput">SOCK_SEQPACKET</code>).
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">io_service::stopped()</code> function that can be used
          to determine whether the <code class="computeroutput">io_service</code> has stopped (i.e. a <code class="computeroutput">reset()</code>
          call is needed prior to any further calls to <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>,
          <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code>).
        </li>
<li class="listitem">
          Reduced the copying of handler function objects.
        </li>
<li class="listitem">
          Added support for C++0x move construction to further reduce copying of
          handler objects. Move support is enabled when compiling in <code class="literal">-std=c++0x</code>
          mode on g++ 4.5 or higher, or when using MSVC10.
        </li>
<li class="listitem">
          Removed the dependency on OS-provided macros for the well-known IPv4 and
          IPv6 addresses. This should eliminate the annoying "missing braces
          around initializer" warnings.
        </li>
<li class="listitem">
          Reduced the size of <code class="computeroutput">ip::basic_endpoint&lt;&gt;</code> objects (such
          as <code class="computeroutput">ip::tcp::endpoint</code> and <code class="computeroutput">ip::udp::endpoint</code>).
        </li>
<li class="listitem">
          Changed the reactor backends to assume that any descriptors or sockets
          added using <code class="computeroutput">assign()</code> may have been <code class="computeroutput">dup()</code>-ed,
          and so require explicit deregistration from the reactor.
        </li>
<li class="listitem">
          Changed the SSL error category to return error strings from the OpenSSL
          library.
        </li>
<li class="listitem">
          Changed the separate compilation support such that, to use Asio's SSL capabilities,
          you should also include 'asio/ssl/impl/src.hpp` in one source file in your
          program.
        </li>
<li class="listitem">
          Removed the deprecated member functions named <code class="computeroutput">io_service()</code>.
          The <code class="computeroutput">get_io_service()</code> member functions should be used instead.
        </li>
<li class="listitem">
          Removed the deprecated typedefs <code class="computeroutput">resolver_query</code> and <code class="computeroutput">resolver_iterator</code>
          from the <code class="computeroutput">ip::tcp</code>, <code class="computeroutput">ip::udp</code> and <code class="computeroutput">ip::icmp</code>
          classes.
        </li>
<li class="listitem">
          Fixed a compile error on some versions of g++ due to anonymous enums.
        </li>
<li class="listitem">
          Added an explicit cast to the <code class="computeroutput">FIONBIO</code> constant to int to suppress
          a compiler warning on some platforms.
        </li>
<li class="listitem">
          Fixed warnings reported by g++'s <code class="literal">-Wshadow</code> compiler option.
        </li>
</ul></div>
<h4>
<a name="asio.history.h20"></a>
      <span><a name="asio.history.asio_1_4_8"></a></span><a class="link" href="history.html#asio.history.asio_1_4_8">Asio
      1.4.8</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed an integer overflow problem that occurs when <code class="computeroutput">ip::address_v4::broadcast()</code>
          is used on 64-bit platforms.
        </li>
<li class="listitem">
          Fixed a problem on older Linux kernels (where epoll is used without <code class="computeroutput">timerfd</code>
          support) that prevents timely delivery of <code class="computeroutput">deadline_timer</code> handlers,
          after the program has been running for some time.
        </li>
</ul></div>
<h4>
<a name="asio.history.h21"></a>
      <span><a name="asio.history.asio_1_4_7"></a></span><a class="link" href="history.html#asio.history.asio_1_4_7">Asio
      1.4.7</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed a problem on kqueue-based platforms where a <code class="computeroutput">deadline_timer</code>
          may never fire if the <code class="computeroutput">io_service</code> is running in a background
          thread.
        </li>
<li class="listitem">
          Fixed a const-correctness issue that prevented valid uses of <code class="computeroutput">has_service&lt;&gt;</code>
          from compiling.
        </li>
<li class="listitem">
          Fixed MinGW cross-compilation.
        </li>
<li class="listitem">
          Removed dependency on deprecated Boost.System functions (Boost.Asio only).
        </li>
<li class="listitem">
          Ensured <code class="computeroutput">close()</code>/<code class="computeroutput">closesocket()</code> failures are correctly
          propagated.
        </li>
<li class="listitem">
          Added a check for errors returned by <code class="computeroutput">InitializeCriticalSectionAndSpinCount</code>.
        </li>
<li class="listitem">
          Added support for hardware flow control on QNX.
        </li>
<li class="listitem">
          Always use <code class="computeroutput">pselect()</code> on HP-UX, if it is available.
        </li>
<li class="listitem">
          Ensured handler arguments are passed as lvalues.
        </li>
<li class="listitem">
          Fixed Windows build when thread support is disabled.
        </li>
<li class="listitem">
          Fixed a Windows-specific problem where <code class="computeroutput">deadline_timer</code> objects
          with expiry times set more than 5 minutes in the future may never expire.
        </li>
<li class="listitem">
          Fixed the resolver backend on BSD platforms so that an empty service name
          resolves to port number <code class="computeroutput">0</code>, as per the documentation.
        </li>
<li class="listitem">
          Fixed read operations so that they do not accept buffer sequences of type
          <code class="computeroutput">const_buffers_1</code>.
        </li>
<li class="listitem">
          Redefined <code class="computeroutput">Protocol</code> and <code class="computeroutput">id</code> to avoid clashing with
          Objective-C++ keywords.
        </li>
<li class="listitem">
          Fixed a <code class="computeroutput">vector</code> reallocation performance issue that can occur
          when there are many active <code class="computeroutput">deadline_timer</code> objects.
        </li>
<li class="listitem">
          Fixed the kqueue backend so that it compiles on NetBSD.
        </li>
<li class="listitem">
          Fixed the socket <code class="computeroutput">io_control()</code> implementation on 64-bit Mac
          OS X and BSD platforms.
        </li>
<li class="listitem">
          Fixed a Windows-specific problem where failures from <code class="computeroutput">accept()</code>
          are incorrectly treated as successes.
        </li>
<li class="listitem">
          Deprecated the separate compilation header <code class="computeroutput">asio/impl/src.cpp</code>
          in favour of <code class="computeroutput">asio/impl/src.hpp</code>.
        </li>
</ul></div>
<h4>
<a name="asio.history.h22"></a>
      <span><a name="asio.history.asio_1_4_6"></a></span><a class="link" href="history.html#asio.history.asio_1_4_6">Asio
      1.4.6</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Reduced compile times. (Note that some programs may need to add additional
          <code class="computeroutput">#include</code>s, e.g. if the program uses boost::array but does
          not explicitly include <code class="computeroutput">&lt;boost/array.hpp&gt;</code>.)
        </li>
<li class="listitem">
          Reduced the size of generated code.
        </li>
<li class="listitem">
          Refactored <code class="computeroutput">deadline_timer</code> implementation to improve performance.
        </li>
<li class="listitem">
          Improved multiprocessor scalability on Windows by using a dedicated hidden
          thread to wait for timers.
        </li>
<li class="listitem">
          Improved performance of <code class="computeroutput">asio::streambuf</code> with <code class="computeroutput">async_read()</code>
          and <code class="computeroutput">async_read_until()</code>. These read operations now use the
          existing capacity of the <code class="computeroutput">streambuf</code> when reading, rather than
          limiting the read to 512 bytes.
        </li>
<li class="listitem">
          Added optional separate compilation. To enable, include <code class="computeroutput">asio/impl/src.cpp</code>
          in one source file in a program, then build the program with <code class="computeroutput">(BOOST_)ASIO_SEPARATE_COMPILATION</code>
          defined in the project/compiler settings. Alternatively, <code class="computeroutput">(BOOST_)ASIO_DYN_LINK</code>
          may be defined to build a separately-compiled Asio as part of a shared
          library.
        </li>
<li class="listitem">
          Added new macro <code class="computeroutput">(BOOST_)ASIO_DISABLE_FENCED_BLOCK</code> to permit
          the disabling of memory fences around completion handlers, even if thread
          support is enabled.
        </li>
<li class="listitem">
          Reworked timeout examples to better illustrate typical use cases.
        </li>
<li class="listitem">
          Ensured that handler arguments are passed as const types.
        </li>
<li class="listitem">
          Fixed incorrect parameter order in <code class="computeroutput">null_buffers</code> variant of
          <code class="computeroutput">async_send_to</code>.
        </li>
<li class="listitem">
          Ensured unsigned char is used with <code class="computeroutput">isdigit</code> in <code class="computeroutput">getaddrinfo</code>
          emulation.
        </li>
<li class="listitem">
          Fixed handling of very small but non-zero timeouts.
        </li>
<li class="listitem">
          Fixed crash that occurred when an empty buffer sequence was passed to a
          composed read or write operation.
        </li>
<li class="listitem">
          Added missing operator+ overload in <code class="computeroutput">buffers_iterator</code>.
        </li>
<li class="listitem">
          Implemented cancellation of <code class="computeroutput">null_buffers</code> operations on Windows.
        </li>
</ul></div>
<h4>
<a name="asio.history.h23"></a>
      <span><a name="asio.history.asio_1_4_5"></a></span><a class="link" href="history.html#asio.history.asio_1_4_5">Asio
      1.4.5</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved performance.
        </li>
<li class="listitem">
          Reduced compile times.
        </li>
<li class="listitem">
          Reduced the size of generated code.
        </li>
<li class="listitem">
          Extended the guarantee that background threads don't call user code to
          all asynchronous operations.
        </li>
<li class="listitem">
          Changed to use edge-triggered epoll on Linux.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">timerfd</code> for dispatching timers on Linux, when
          available.
        </li>
<li class="listitem">
          Changed to use one-shot notifications with kqueue on Mac OS X and BSD platforms.
        </li>
<li class="listitem">
          Added a bitmask type <code class="computeroutput">ip::resolver_query_base::flags</code> as per
          the TR2 proposal. This type prevents implicit conversion from <code class="computeroutput">int</code>
          to <code class="computeroutput">flags</code>, allowing the compiler to catch cases where users
          incorrectly pass a numeric port number as the service name.
        </li>
<li class="listitem">
          Added <code class="computeroutput">#define NOMINMAX</code> for all Windows compilers. Users can
          define <code class="computeroutput">(BOOST_)ASIO_NO_NOMINMAX</code> to suppress this definition.
        </li>
<li class="listitem">
          Fixed a bug where 0-byte asynchronous reads were incorrectly passing an
          <code class="computeroutput">error::eof</code> result to the completion handler.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">io_control()</code> member functions to always call
          <code class="computeroutput">ioctl</code> on the underlying descriptor when modifying blocking
          mode.
        </li>
<li class="listitem">
          Changed the resolver implementation so that it no longer requires the typedefs
          <code class="computeroutput">InternetProtocol::resolver_query</code> and <code class="computeroutput">InternetProtocol::resolver_iterator</code>,
          as neither typedef is part of the documented <code class="computeroutput">InternetProtocol</code>
          requirements. The corresponding typedefs in the <code class="computeroutput">ip::tcp</code>,
          <code class="computeroutput">ip::udp</code> and <code class="computeroutput">ip::icmp</code> classes have been deprecated.
        </li>
<li class="listitem">
          Fixed out-of-band handling for reactors not based on <code class="computeroutput">select()</code>.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">(BOOST_)ASIO_DISABLE_THREADS</code> macro that allows Asio's
          threading support to be independently disabled.
        </li>
<li class="listitem">
          Minor documentation improvements.
        </li>
</ul></div>
<h4>
<a name="asio.history.h24"></a>
      <span><a name="asio.history.asio_1_4_4"></a></span><a class="link" href="history.html#asio.history.asio_1_4_4">Asio
      1.4.4</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new HTTP Server 4 example illustrating the use of stackless coroutines
          with Asio.
        </li>
<li class="listitem">
          Changed handler allocation and invocation to use <code class="computeroutput">boost::addressof</code>
          to get the address of handler objects, rather than applying <code class="computeroutput">operator&amp;</code>
          directly.
        </li>
<li class="listitem">
          Restricted MSVC buffer debugging workaround to 2008, as it causes a crash
          with 2010 beta 2.
        </li>
<li class="listitem">
          Fixed a problem with the lifetime of handler memory, where Windows needs
          the <code class="computeroutput">OVERLAPPED</code> structure to be valid until both the initiating
          function call has returned and the completion packet has been delivered.
        </li>
<li class="listitem">
          Don't block signals while performing system calls, but instead restart
          the calls if they are interrupted.
        </li>
<li class="listitem">
          Documented the guarantee made by strand objects with respect to order of
          handler invocation.
        </li>
<li class="listitem">
          Changed strands to use a pool of implementations, to make copying of strands
          cheaper.
        </li>
<li class="listitem">
          Ensured that kqueue support is enabled for BSD platforms.
        </li>
<li class="listitem">
          Added a <code class="computeroutput">boost_</code> prefix to the <code class="computeroutput">extern "C"</code>
          thread entry point function.
        </li>
<li class="listitem">
          In <code class="computeroutput">getaddrinfo</code> emulation, only check the socket type (<code class="computeroutput">SOCK_STREAM</code>
          or <code class="computeroutput">SOCK_DGRAM</code>) if a service name has been specified. This
          should allow the emulation to work with raw sockets.
        </li>
<li class="listitem">
          Added a workaround for some broken Windows firewalls that make a socket
          appear bound to 0.0.0.0 when it is in fact bound to 127.0.0.1.
        </li>
<li class="listitem">
          Applied a fix for reported excessive CPU usage under Solaris.
        </li>
<li class="listitem">
          Added some support for platforms that use older compilers such as g++ 2.95.
        </li>
</ul></div>
<h4>
<a name="asio.history.h25"></a>
      <span><a name="asio.history.asio_1_4_3"></a></span><a class="link" href="history.html#asio.history.asio_1_4_3">Asio
      1.4.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new ping example to illustrate the use of ICMP sockets.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">buffered*_stream&lt;&gt;</code> templates to treat 0-byte
          reads and writes as no-ops, to comply with the documented type requirements
          for <code class="computeroutput">SyncReadStream</code>, <code class="computeroutput">AsyncReadStream</code>, <code class="computeroutput">SyncWriteStream</code>
          and <code class="computeroutput">AsyncWriteStream</code>.
        </li>
<li class="listitem">
          Changed some instances of the <code class="computeroutput">throw</code> keyword to <code class="computeroutput">boost::throw_exception()</code>
          to allow Asio to be used when exception support is disabled. Note that
          the SSL wrappers still require exception support.
        </li>
<li class="listitem">
          Made Asio compatible with the OpenSSL 1.0 beta.
        </li>
<li class="listitem">
          Eliminated a redundant system call in the Solaris /dev/poll backend.
        </li>
<li class="listitem">
          Fixed a bug in resizing of the bucket array in the internal hash maps.
        </li>
<li class="listitem">
          Ensured correct propagation of the error code when a synchronous accept
          fails.
        </li>
<li class="listitem">
          Ensured correct propagation of the error code when a synchronous read or
          write on a Windows <code class="computeroutput">HANDLE</code> fails.
        </li>
<li class="listitem">
          Fixed failures reported when <code class="computeroutput">_GLIBCXX_DEBUG</code> is defined.
        </li>
<li class="listitem">
          Fixed custom memory allocation support for timers.
        </li>
<li class="listitem">
          Tidied up various warnings reported by g++.
        </li>
<li class="listitem">
          Various documentation improvements, including more obvious hyperlinks to
          function overloads, header file information, examples for the handler type
          requirements, and adding enum values to the index.
        </li>
</ul></div>
<h4>
<a name="asio.history.h26"></a>
      <span><a name="asio.history.asio_1_4_2"></a></span><a class="link" href="history.html#asio.history.asio_1_4_2">Asio
      1.4.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implement automatic resizing of the bucket array in the internal hash maps.
          This is to improve performance for very large numbers of asynchronous operations
          and also to reduce memory usage for very small numbers. A new macro <code class="computeroutput">(BOOST_)ASIO_HASH_MAP_BUCKETS</code>
          may be used to tweak the sizes used for the bucket arrays. (N.B. this feature
          introduced a bug which was fixed in Asio 1.4.3 / Boost 1.40.)
        </li>
<li class="listitem">
          Add performance optimisation for the Windows IOCP backend for when no timers
          are used.
        </li>
<li class="listitem">
          Prevent locale settings from affecting formatting of TCP and UDP endpoints.
        </li>
<li class="listitem">
          Fix a memory leak that occurred when an asynchronous SSL operation's completion
          handler threw an exception.
        </li>
<li class="listitem">
          Fix the implementation of <code class="computeroutput">io_control()</code> so that it adheres
          to the documented type requirements for IoControlCommand.
        </li>
<li class="listitem">
          Fix incompatibility between Asio and ncurses.h.
        </li>
<li class="listitem">
          On Windows, specifically handle the case when an overlapped <code class="computeroutput">ReadFile</code>
          call fails with <code class="computeroutput">ERROR_MORE_DATA</code>. This enables a hack where
          a <code class="computeroutput">windows::stream_handle</code> can be used with a message-oriented
          named pipe.
        </li>
<li class="listitem">
          Fix system call wrappers to always clear the error on success, as POSIX
          allows successful system calls to modify errno.
        </li>
<li class="listitem">
          Don't include termios.h if <code class="computeroutput">(BOOST_)ASIO_DISABLE_SERIAL_PORT</code>
          is defined.
        </li>
<li class="listitem">
          Cleaned up some more MSVC level 4 warnings.
        </li>
<li class="listitem">
          Various documentation fixes.
        </li>
</ul></div>
<h4>
<a name="asio.history.h27"></a>
      <span><a name="asio.history.asio_1_4_1"></a></span><a class="link" href="history.html#asio.history.asio_1_4_1">Asio
      1.4.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved compatibility with some Windows firewall software.
        </li>
<li class="listitem">
          Ensured arguments to <code class="computeroutput">windows::overlapped_ptr::complete()</code> are
          correctly passed to the completion handler.
        </li>
<li class="listitem">
          Fixed a link problem and multicast failure on QNX.
        </li>
<li class="listitem">
          Fixed a compile error in SSL support on MinGW / g++ 3.4.5.
        </li>
<li class="listitem">
          Drop back to using a pipe for notification if eventfd is not available
          at runtime on Linux.
        </li>
<li class="listitem">
          Various minor bug and documentation fixes.
        </li>
</ul></div>
<h4>
<a name="asio.history.h28"></a>
      <span><a name="asio.history.asio_1_4_0"></a></span><a class="link" href="history.html#asio.history.asio_1_4_0">Asio
      1.4.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Enhanced CompletionCondition concept with the signature <code class="computeroutput">size_t CompletionCondition(error_code
          ec, size_t total)</code>, where the return value indicates the maximum
          number of bytes to be transferred on the next read or write operation.
          (The old CompletionCondition signature is still supported for backwards
          compatibility).
        </li>
<li class="listitem">
          New <code class="computeroutput">windows::overlapped_ptr</code> class to allow arbitrary overlapped
          I/O functions (such as <code class="computeroutput">TransmitFile</code>) to be used with Asio.
        </li>
<li class="listitem">
          On recent versions of Linux, an <code class="computeroutput">eventfd</code> descriptor is now
          used (rather than a pipe) to interrupt a blocked select/epoll reactor.
        </li>
<li class="listitem">
          Added const overloads of <code class="computeroutput">lowest_layer()</code>.
        </li>
<li class="listitem">
          Synchronous read, write, accept and connect operations are now thread safe
          (meaning that it is now permitted to perform concurrent synchronous operations
          on an individual socket, if supported by the OS).
        </li>
<li class="listitem">
          Reactor-based <code class="computeroutput">io_service</code> implementations now use lazy initialisation
          to reduce the memory usage of an <code class="computeroutput">io_service</code> object used only
          as a message queue.
        </li>
</ul></div>
<h4>
<a name="asio.history.h29"></a>
      <span><a name="asio.history.asio_1_2_0"></a></span><a class="link" href="history.html#asio.history.asio_1_2_0">Asio
      1.2.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for serial ports.
        </li>
<li class="listitem">
          Added support for UNIX domain sockets.
        </li>
<li class="listitem">
          Added support for raw sockets and ICMP.
        </li>
<li class="listitem">
          Added wrappers for POSIX stream-oriented file descriptors (excluding regular
          files).
        </li>
<li class="listitem">
          Added wrappers for Windows stream-oriented <code class="computeroutput">HANDLE</code>s such as
          named pipes (requires <code class="computeroutput">HANDLE</code>s that work with I/O completion
          ports).
        </li>
<li class="listitem">
          Added wrappers for Windows random-access <code class="computeroutput">HANDLE</code>s such as files
          (requires <code class="computeroutput">HANDLE</code>s that work with I/O completion ports).
        </li>
<li class="listitem">
          Added support for reactor-style operations (i.e. they report readiness
          but perform no I/O) using a new <code class="computeroutput">null_buffers</code> type.
        </li>
<li class="listitem">
          Added an iterator type for bytewise traversal of buffer sequences.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">read_until()</code> and <code class="computeroutput">async_read_until()</code>
          overloads that take a user-defined function object for locating message
          boundaries.
        </li>
<li class="listitem">
          Added an experimental two-lock queue (enabled by defining <code class="computeroutput">(BOOST_)ASIO_ENABLE_TWO_LOCK_QUEUE</code>)
          that may provide better <code class="computeroutput">io_service</code> scalability across many
          processors.
        </li>
<li class="listitem">
          Various fixes, performance improvements, and more complete coverage of
          the custom memory allocation support.
        </li>
</ul></div>
<h4>
<a name="asio.history.h30"></a>
      <span><a name="asio.history.asio_1_0_0"></a></span><a class="link" href="history.html#asio.history.asio_1_0_0">Asio
      1.0.0</a>
    </h4>
<p>
      First stable release of Asio.
    </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2018 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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